Synthesis and Biological Evaluation of Imidazopyridine-Isatin Hybrids as Inhibitors of Leishmania major Growth

Introduction: More than 20 different species of Leishmania cause leishmaniasis, a multifaceted disease that ranges from mild cutaneous lesions to fatal visceral forms. Methods: Sixteen novel hybrids were designed by covalently linking an imidazo1,2- a pyridine core to an isatin scaffold via a hydrazide linker, and their in vitro anti-promastigote, anti-amastigote, cytotoxicity, and molecular docking profiles were evaluated, with folate-rescue assays used to assess the anti-folate mechanism. Results: Several compounds showed potent anti-leishmanial activity compared to miltefosine, with the lead compound 5b exhibiting strong anti-promastigote (IC 5 0 = 0.84 ± 0.06 μM) and anti-amastigote (IC 5 0 = 1.28 ± 0.18 μM) activities, significantly surpassing miltefosine. Folic and folinic acids reversed the activity of 5b , confirming an anti-folate mechanism similar to that of the Lm-PTR1 inhibitor trimethoprim. The most active compounds showed higher selectivity indices (SI = 12.74) than miltefosine (SI = 438.03), and docking against Lm-PTR1 provided a plausible explanation for their potency, while in silico predictions indicated favorable drug-likeness and pharmacokinetic properties. Conclusion: These findings highlight a promising new chemotype targeting the leishmanial folate pathway and expand the chemical diversity available for anti-leishmanial drug development. Keywords: neglected tropical diseases, leishmaniasis, molecular modeling, anti-folate mechanism, imidazo1,2- a pyridine, isatin